Sumio Oe

Further test of the isolated pentagon rule: Thermodynamic and kinetic stabilities of C84 fullerene isomers

Thermodynamic and kinetic stabilities of 73 C84 fullerene isomers were estimated from the MM3 heats of formation and the recently defined bond resonance energies (BREs), respectively. The BRE represents the contribution of a given π bond in a molecule to the topological resonance energy (TRE). All π bonds shared by two pentagons turned out to be highly reactive without exceptions. C84 fullerene isomers with such π bonds must be incapable of survival during harsh synthetic processes. Thus, the isolated pentagon rule (IPR) proved to be applicable to such large fullerene cages. For sufficiently large fullerenes like C84, some isolated‐pentagon isomers are also predicted to be very unstable with highly antiaromatic π bonds.

Conformation-determining factors for complexes of 18-crown-6 with cations

Abstract Raman and IR spectra of complexes of 18-crown-6 with cations were measured for their aqueous solutions and crystals. A C s symmetry conformation of 18-crown-6 in its complexes with divalent cations was deduced, based on the solvent effect on the spectra of 18-crown-6 and also normal vibration calculation. Conformation analyses by spectral patterns revealed that the electric charge of captured cations determines the conformation of 18-crown-6 in complexes in solutions, while that of the crystals is affected by the ionic diameter of captured cations.

RAISON D'ETRE OF APPARENTLY ANTIAROMATIC 1,2-DITHIIN DERIVATIVES IN NATURE

Abstract Although living organisms tend to avoid synthesizing antiaromatic molecules because of their thermodynamic and kinetic instability, some composite plants synthesize apparently antiaromatic 1,2-dithiin derivatives. Molecular orbital calculations at the HF/6-31G** level revealed that the antiaromaticity of the 1,2-dithiin ring is markedly reduced by assuming a non-planar molecular structure. It was found that both 1,2- and 1,4-dithiin rings are essentially nonaromatic with the Dewar resonance energies being close to zero. This must be the primary reason why 1,2-dithiins occur in nature.

Weighted Homo-Lumo Energy Separations for the Polyene References of Fullerenes with Up to 100 Carbon Atoms

Abstract The T value represents the HOMO-LUMO energy separation of a ∊-electronic system weighted with the number of conjugated atoms. We found that this value is kept almost constant for the polyene references defined graph-theoretically for isolated-pentagon isomers of fullerenes with up to 100 carbon atoms. on this numerical basis, the T value can safely be considered as a realistic index of kinetic stability or chemical inertness for all fullerenes without abutting pentagons.

Microwave spectroscopy of the PBr radical in the X (3)Sigma(-) state.

The microwave spectrum of the PBr radical in the X (3)Sigma(-) ground electronic state has been observed by a source modulated spectrometer. The PBr radical was generated in a free space cell by an acdc glow discharge in a mixture of PBr(3) with He andor H(2). A spectrum with three spin components for each of the two isotopomers, P(79)Br and P(81)Br, was observed. The spectrum showed hyperfine splitting caused by interactions due to both bromine and phosphorus nuclei. The molecular constants including the magnetic hyperfine and nuclear quadrupole hyperfine interaction constants were determined by analyzing the observed spectrum. The spin density of the unpaired electrons was estimated from the observed hyperfine coupling constants to be 85.4% and 16.3% on the phosphorus and bromine atoms, respectively.

Raman spectroscopic study of characteristic conformations of bipyridines adsorbed on active electrode surface

Abstract Surface enhanced Raman scattering spectra have been measured for bipyridine/potassium chloride/methanol systems: each bipyridine shows characteristic spectral change due to adsorption on the active electrode surface. Spectra of 2,3′-bipyridine, 2,4′-bipyridine and 4,4′-bipyridine adsorbed on the surface resemble those of corresponding crystals; spectra of surface adsorbed 2,2′-bipyridine are very different from those of the crystal, the structure having cis conformation around the CC single bond being dominant for adsorbed 2,2′-bipyridine. Therefore, locations of the two nitrogen atoms in the bipyridine ring affect the conformation of bipyridines adsorbed on the working electrode surface.

Microwave spectrum, barrier to internal rotation of CF3, structure, and ab initio calculation of 1,1,1,2,2-pentafluoropropane

Abstract The microwave spectrum of 1,1,1,2,2-pentafluoropropane CF 3 CF 2 CH 3 (HFC 245cb) has been studied for the first time using both a Stark modulation and Fourier transform microwave spectrometer. A least-squares analysis of the observed a- and b-type transition frequencies gave rotational and centrifugal distortion constants for the vibrational ground state as follows: A=2715.9979(2) MHz , B=1831.3817(2) MHz , C=1810.6342(2) MHz , Δ J =0.112(3) kHz , Δ JK =0.033(3) kHz , Δ K =−0.0066(19) kHz, δ J =0.0030(2) kHz , δ K =−0.73(9) kHz . The barrier height to internal rotation of the CF 3 group has been determined to be V 3 =2.86±0.72 kcal / mol . A reasonable molecular structure has been derived from the observed rotational constants combining with ab initio calculation. These barrier height and structural parameters are compared with those of other related molecules.